Diagnostic Considerations

Keratoconus should be differentiated from other causes of corneal steepening and irregular oblique astigmatism, imprecise variable subjective refractions, and non-inflammatory central corneal scarring. These may include corneal surgery, healed infections, and trauma.

Stromal striations similar to Vogt striae occur when corneas swell (rather than thin) from either hypoxia (associated with wear of contact lenses) or with early Fuchs corneal dystrophy.

Iron depositions in the basal epithelium (similar to a Fleischer ring) can occur in any area of relative depression in the corneal surface (eg, in association with pterygium, surgical scars, and central depressions from refractive surgery).

Pellucid marginal degeneration is often considered a variant of keratoconus. In pellucid marginal degeneration, corneal thinning occurs about 1 mm above the inferior limbus, resulting in advanced against-the-rule corneal astigmatism that may be observed on corneal topography or tomography.

Terrien marginal corneal degeneration is a mildly inflammatory disease, usually of the superior limbus. This disease can also induce irregular against-the-rule astigmatism and corneal thinning (often with vascularization and lipid deposits).

Keratoglobus is an extremely rare corneal disease in which the entire cornea, from limbus to limbus, thins, sometimes to the point where spontaneous perforation becomes possible. Keratoglobus is probably unrelated to keratoconus.

Posterior keratoconus is another extremely rare disease (or nonexistent), in which the posterior corneal surface suffers a loss of substance. This condition is probably unrelated to keratoconus.

Posterior polymorphous corneal dystrophy can lead to keratoconic-like steep cornea.^[34]

Differential Diagnoses

Contact Lens Complications
Corneal ectasia due to refractive surgery
Diplopia (Double Vision)
Interstitial Keratitis
Pellucid Marginal Degeneration (PMD)

Workup

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An optic section of a keratoconic cornea shows corneal thinning. Vogt striae and some scarring can also be seen centrally; superiorly, a small (brown) section of the Fleischer ring is noted.
The fluorescein pattern of a rather flat-fitted rigid contact lens on an advanced keratoconic cornea.

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Author

Karen K Yeung, OD, FAAO Senior Optometrist, UCLA Arthur Ashe Student Health and Wellness Center; Clinical Assistant Professor, College of Optometry, Western University of Health Sciences

Karen K Yeung, OD, FAAO is a member of the following medical societies: American Academy of Optometry

Disclosure: Nothing to disclose.

Coauthor(s)

Barry A Weissman, OD, PhD, FAAO Retired Professor of Optometry, Southern California College of Optometry at Marshall B Ketchum University; Professor Emeritus of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine

Barry A Weissman, OD, PhD, FAAO is a member of the following medical societies: American Academy of Optometry, American Optometric Association, California Optometric Society, International Society for Contact Lens Research

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Christopher J Rapuano, MD Professor, Department of Ophthalmology, Sidney Kimmel Medical College of Thomas Jefferson University; Director of the Cornea Service, Wills Eye Hospital

Christopher J Rapuano, MD is a member of the following medical societies: American Academy of Ophthalmology, American Ophthalmological Society, American Society of Cataract and Refractive Surgery, Contact Lens Association of Ophthalmologists, Cornea Society, Eye Bank Association of America, International Society of Refractive Surgery

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: AAO; OMIC; American Society of Ophthalmic Trauma (ASOT); Avellino, Baxis; Bio-Tissue; Celularity; Dompe; Emmecell; Glaukos; Kala; Oyster Point; Sun Ophthalmics; Tarsus; TearLab<br/>Serve(d) as a speaker or a member of a speakers bureau for: Glaukos; Dompe; Bio-Tissue<br/>Received research grant from: Glaukos<br/>Received income in an amount equal to or greater than $250 from: AAO; OMIC; Baxis; Bio-Tissue; Cellularity; Dompe; Glaukos; Kala; Sun Ophthalmics; TearLab<br/>stock options for: RPS, Fount Bio.

Chief Editor

Hampton Roy, Sr, MD † Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Hampton Roy, Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

Additional Contributors

Fernando H Murillo-Lopez, MD Senior Surgeon, Unidad Privada de Oftalmologia CEMES

Fernando H Murillo-Lopez, MD is a member of the following medical societies: American Academy of Ophthalmology

Disclosure: Nothing to disclose.

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